The present invention pertains to a workpiece guide for sewing machines and particularly to a guide that is effective in removing the curling or rolling of the sides of the pieces of fabric forming the workpiece. As is well known to those conversant in the sewing art, when joining superposed layers of fabric by seaming, it is important that the edges of said layers, along which the seam is to be incorporated, be maintained in alignment even when said edges may have profiles that are not identical.
Workpiece guides for maintaining alignment of the edges of superposed layers of fabric are well known and are commonly formed by a plurality of vertically aligned plate elements which are spaced to define channels or passages therebetween and which extend in planes parallel with the worksurface of the machine. These plate elements are interconnected by a support member having a surface extending perpendicular to the machine's worksurface and which define a guide wall within each of the passages that is adapted to engage the edge of a layer of fabric and guide the same toward the stitching zone.
The number of plate elements forming a workpiece guide are governed by the number of layers of fabric which are to be joined by seaming, the consistency of the material forming the pieces of fabric, and the diversity and complexity of the edge configurations to be sewn. In particular, in a guide having a plurality of passages, the number of plate elements should be such as to form the same number of channels or passages as there are pieces of fabric to be joined so that said pieces will advance separately in the direction of the sewing zone. The ability of the workpiece guide to maintain the pieces of fabric to be joined in separation as they approach the stitching instrumentalities and at the same time cause the edges thereof to engage their respective guide wall within the guide provides the means for aligning and maintaining alignment of the edges as they enter the sewing zone. This separation between the individual pieces of fabric is necessary in order to automatically align the edges as required even though said pieces may have configurations that differ from one another. In the case of simply providing a seam along the edge of a single piece of fabric regardless of its configuration a guide may be utilized having a single passage which is enclosed by one upper plate member and the worksurface itself or by two plate members. The height of each passage should correspond to the thickness of the fabric which is inserted therein so that said fabric will be adequately spread or flattened in order that its edge will properly engage its respective guide wall. Independent advance of the separate pieces of fabric in contact with their respective guide walls provided in each passage is possible because a portion of said pieces are located beneath the presser foot of the sewing machine which cooperates with the machine's transport device or so-called feed dogs that are effective in advancing the pieces along the sewing axis.
The combined action provided by the presser foot and the feed dogs is concentrated on a limited portion of the pieces of fabric that determines a point laterally disposed relative to the sewing axis and applies a rotating force on said pieces that is effective in causing their edges to maintain engagement with their respective guide walls. Actually the effect of advancement of the pieces of fabric outwardly from the guide and sewing axis where they frictionally engage the worksurface of the machine creates a breaking action on said pieces that continually urges the edges thereof to maintain contact with their respective guide wall within said guide. The upper plate element serves to maintain the upper piece of fabric in its intended path of travel by preventing any possible displacement thereof in an upwardly direction or from becoming folded over. The intermediate plate serves the same function on the lower piece of fabric and as the respective guide walls for each piece of fabric are normally in vertical alignment, they are effective in causing the workpiece to enter the sewing zone with the edges of each piece in required alignment even though one piece may not have the same edge configuration as the other. Advancement of the fabric pieces in their respective passages by the feed dogs presents a problem when the pieces forming the workpiece are exceptionally thin and of light weight construction for the rotating force referred to above is substantially less pronounced on such fabric whereby it becomes more difficult to maintain the separate pieces in contact with their respective guide walls which, of course, results in a further problem of obtaining and maintaining adequate alignment of said edges prior to their entry into the sewing zone.
A further problem occurs in the case of knitted fabric which because of the well known structure of the fabric, any longitudinal traction applied to its edges accentuates its tendency to roll or curl over and thus change its intended shape and structure. Although the provision of braking elements such as follower clips, applied to the trailing edge of the pieces of fabric improves the operational register between the piece and its guide wall, the tendency of the edge to be sewn to curl or roll is enhanced because it is stretched and elongated to a greater extent than the remainder of the fabric.
This disadvantage is most frequently encountered when dealing with knitted fabrics which have a far greater degree of stretch than other fabrics. The developed curl or roll at the edge of the fabric to be sewn is usually rejected by the guide. In other words, the fabric develops at its edge a double or triple thickness which is such as to prevent it from passing through its respective passage in the guide or, if it manages to enter said passage, the seam would be incorrectly formed and would result in a deformity of the intended edge configuration of the sewn piece. Workpiece guides are known which are adapted to correct the rolling over condition of fabric edges before they enter the passages of said guides; however, such known guides have a structural design that is intended for vertical sewing machines only so as to influence pieces of fabric which extend and are caused to advance to the stitching instrumentalities in a vertical manner in order to provide ample clearance surrounding them. These guides are also designed so as to permit manual intervention on the part of the operator so as to effect accurate guiding of the pieces of fabric in the direction of the sewing zone. Consequently, these known types of guides are not adapted to accurately control pieces of fabric in modern sewing machines which are capable of running at high speed. Additionally, these guides would be inadequate if applied to sewing machines utilizing automatic operating cycles and especially when the workpieces are formed from pieces of fabric that are of thin and lightweight construction which are subject to curling or rolling over of the edges.